Authorities say at least 30 detainees escaped from a prison in southern Yemen Thursday after a bomb exploded at the site.

Police say at least four detainees were injured in the blast.

Police say the detainees belong to the southern secessionist movement. Some of them may have been arrested following a protest.

It is unclear if the explosive device was thrown by police or by an inmate.

Meanwhile, secessionists say police shot and killed one protester and injured at least three others in the southern city of Radfan. They say law enforcement authorities opened fire to disperse a protest.

There has been an increase in clashes between separatists and security forces in the south in recent months.

Separatists complain that the north discriminates against them and exploits the natural resources of the south, which holds most of Yemen's oil reserves. They want to reverse a 1990 deal that unified Yemen's northern and southern regions.